Spam is a common term for unsolicited and abusive electronic communications that are indiscriminately broadcast to recipients. Spam can quickly overtake email inboxes, online guest books, forums, submission forms, and other similar electronic communication forums. One reason that spam is so prevalent is that many people who send spam employ internet robots (also referred to as bots or spambots) that are software applications to run automated tasks for collecting recipient information (e.g., email addresses or forum submission websites) and sending or posting spam content to those recipients. In another example, spambots may automatically sign up for available email addresses, which can then be used to send spam to other recipients.
In order to curtail or limit the amount of spam that can be posted to these forums, some sort of logical gatekeeper is typically employed to try to prevent the spambots from automatically accessing recipient information and/or posting spam. One common type of logical gatekeeper process is known as CAPTCHA, which stands for Completely Automated Public Turing test to tell Computers and Humans Apart. In essence, a CAPTCHA test requires a response that presumably cannot be generated by a computer. One common type of CAPTCHA test displays distorted letters which may be read by a human user, but are difficult for a computer to decipher. Hence, a correct response to the CAPTCHA test is assumed to be from a human, rather than a computer.
However, computer programmers have found ways to improve the success rate of computer responses to CAPTCHA tests. Consequently, spamming mechanisms are able to employ more sophisticated response techniques to bypass or obtain access through conventional CAPTCHA testing processes.
In order to compensate for the increased abilities of computer programs to deal with CAPTCHA tests, the words, codes, or images used in the CAPTCHA tests are getting more and more distorted and difficult to determine, regardless of whether the user is a human or a spambot. Unfortunately, arbitrarily increasing the difficulty of CAPTCHA tests results in usability issues which frustrate and sometimes prevent legitimate use by actual human users.